The fabrication of an integrated circuit, display or disc memory generally employs numerous processing steps. Each process step must be carefully monitored in order to provide an operational device. Throughout the imaging process, deposition and growth process, etching and masking process, etc., it is critical, for example, that temperature, gas flow, vacuum, pressure, chemical, gas or plasma composition and exposure distance be carefully controlled during each step. Careful attention to the various processing conditions involved in each step is a requirement of optimal semiconductor or thin film processes. Any deviation from optimal processing conditions may cause the ensuing integrated circuit or device to perform at a substandard level or, worse yet, fail completely.
Within a processing chamber, processing conditions vary. The variations in processing conditions such as temperature, gas flow rate and/or gas composition greatly affect the formation and, thus, the performance of the integrated circuit. Using a sensor having a substrate that is of the same or similar material as the integrated circuit or other device to measure the processing conditions provides the most accurate measure of the conditions because the material properties of the substrate are the same as those of the actual circuits that will be processed. Gradients and variations exist throughout the chamber for virtually all process conditions. These gradients, therefore, also exist across the surface of a substrate, as well as below and above it. In order to precisely control processing conditions at the wafer, it is critical that measurements be taken upon the wafer and are available in real time to an automated control system or operator to readily optimize the chamber processing conditions. Processing conditions include any parameter used to control semiconductor or other device fabrication or any condition a manufacturer would desire to monitor.
One technique for monitoring process conditions in-situ makes use of a measuring device having sensors incorporated onto a substrate similar to the wafers that are processed in the chamber. US publication No. 20060174720 discloses an example of a measuring device incorporating a substrate with sensors that measure the processing conditions that a wafer may undergo during manufacturing. The substrate can be inserted into a processing chamber by a robot and the measuring device can transmit the conditions in real time or store the conditions for subsequent analysis. Sensitive electronic components of the device can be distanced or isolated from the most deleterious processing conditions in order to increase the accuracy, operating range, and reliability of the device.
Monitoring etch conditions, e.g., the temperature, in-situ during an etch process (e.g., a plasma etch) using a sensor wafer is particularly problematic since the sensor wafer is subject to etching during monitoring of the process conditions in the chamber. An unprotected sensor wafer is therefore subject to attack, e.g., by silicon etch chemistry or plasma bombardment in an etch environment. Current sensor wafers use a silicon cover to protect the sensors and best simulate the workpieces being etched. However, when the silicon cover is subjected to the etch process black or white silicon is produced. The black or white silicon contamination can lead to particle generation, which is undesirable in the process chamber.
Some prior art sensor wafers based on silicon wafer substrates have used standard thin film materials such as polyimide or silicon oxide coatings to protect the sensor wafer from etching during measurement in plasma etch conditions. However, the polyimide and silicon oxide coatings have limited resistance to etch under poly and through-silicon via (TSV) etch conditions. For a sensor wafer used in a plasma etch chamber it would be desirable for the protective coating to last at least 10 hours. Experience with such coated wafers has shown that SiO2 and polyimide coatings cannot last this long unless they are extremely thick, e.g., approximately 10 μm thick for SiO2 and at least 100 μm thick for polyimide. Unfortunately, a thicker coating can introduce artifacts in temperature measurement and may also warp the wafer. Thus, there is an unmet need for a sensor wafer that can survive for 10 hours of cumulative exposure to a plasma etch environment.
In addition to being etch resistant, it would be further desirable for the coating to be relatively thin, non-contaminating, and strongly adhering to the cover and substrate material.
It is within this context that embodiments of the present invention arise.